Simplify implementation of print_chain.

pep-0344.txt

@@ -295,20 +295,13 @@ Enhanced Reporting
     or __context__ respectively.  Here is a sketch of the procedure:
     
         def print_chain(exc):
-            chain = []
-            link = None
-            while exc:
-                chain.append((exc, link))
-                if exc.__cause__:
-                    exc, link = exc.__cause__, 'The above exception...'
-                else:
-                    exc, link = exc.__context__, 'During handling...'
-            for exc, link in reversed(chain):
-                print_exc(exc)
-                if link:
-                    print
-                    print link
-                    print
+            if exc.__cause__:
+                print_chain(exc.__cause__)
+                print '\nThe above exception was the direct cause...'
+            elif exc.__context__:
+                print_chain(exc.__context__)
+                print '\nDuring handling of the above exception, ...'
+            print_exc(exc)
 
     In the 'traceback' module, the format_exception, print_exception,
     print_exc, and print_last functions will be updated to accept an